The present invention relates to a displacement control valve for controlling displacement of a variable displacement compressor, which is used in a refrigerant circuit of a vehicle air conditioner and changes the displacement based on the pressure in a crank chamber.
A typical refrigerant circuit (refrigeration cycle) in a vehicle air-conditioner includes a condenser, an expansion valve, which functions as a decompression device, an evaporator and a compressor. The compressor draws refrigerant gas from the evaporator, then, compresses the gas and discharges the compressed gas to the condenser. The evaporator performs heat exchange between the refrigerant in the refrigerant circuit and the air in the passenger compartment. The heat of air at the evaporator is transmitted to the refrigerant flowing through the evaporator in accordance with the thermal load or the cooling load. Therefore, the pressure of refrigerant gas at the outlet of or the downstream portion of the evaporator represents the cooling load.
Variable displacement compressors are widely used in vehicles. Such compressors include a displacement control mechanism that operates to maintain the pressure at the outlet of the evaporator, or the suction pressure, at a predetermined target level (target suction pressure). The control mechanism feedback controls the displacement of the compressor, or the inclination angle of a swash plate, by referring to the suction pressure such that the flow rate of refrigerant in the refrigerant circuit corresponds to the cooling load.
A typical displacement mechanism includes a displacement control valve, which is called an internally controlled valve. The internally controlled valve detects the suction pressure by means of a pressure sensitive member such as a bellows and a diaphragm. The internally controlled valve moves a valve body by the displacement of the pressure-sensing member to adjust the valve opening size. Accordingly, the pressure in a swash plate chamber (a crank chamber), or the crank chamber pressure is changed, which changes the inclination of the swash plate.
However, an internally controlled valve that has a simple structure and a single target suction pressure cannot respond to the changes in air conditioning demands. Therefore, there exist control valves having a target suction pressure that can be changed by external electrical control. A typical electrically controlled control valve is a combination of an internally controlled valve and an actuator such as an electromagnetic solenoid, which generates an electrically controlled force. In such a control valve, mechanical spring force, which acts on the pressure-sensing member, is externally controlled to change the target suction pressure.
In a displacement control procedure in which the suction pressure is used as a reference, changing of the target suction pressure by electrical control does not always quickly change the actual suction pressure to the target suction pressure. This is because whether the actual suction pressure quickly seeks a target suction pressure when the target suction pressure is changed depends greatly on the cooling load on the evaporator. Therefore, even if the target suction pressure is finely and continuously controlled by controlling the current to the control valve, changes in the compressor displacement are likely to be too slow or too sudden.
Accordingly, it is an objective of the present invention to provide a control valve for a variable displacement compressor that improves the controllability and response of displacement control.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve for controlling the displacement of a variable displacement compressor used in a refrigerant circuit is provided. The compressor includes a crank chamber and a pressure control passage, which is connected to the crank chamber. The displacement of the compressor changes in accordance with the pressure in the crank chamber. The control valve adjusts the opening size of the pressure control passage, thereby controlling the pressure in the crank chamber. The control valve includes a valve housing, a valve body, a pressure-sensing chamber, a pressure-sensing member, a first urging member, a second urging member and an actuator. The valve body is accommodated in the valve housing. The valve body adjusts the opening size of the pressure control passage. The pressure-sensing chamber is defined in the valve housing. The pressure-sensing member divides the pressure-sensing chamber into a first pressure chamber and a second pressure chamber. The first pressure chamber is exposed to the pressure at a first pressure monitoring point, which is located in the refrigerant circuit. The second pressure chamber is exposed to the pressure at a second pressure monitoring point, which is located in the refrigerant circuit. The pressure at the first pressure monitoring point is higher than the pressure at the second pressure monitoring point. The pressure-sensing member actuates the valve body in accordance with the pressure difference between the pressure chambers, thereby controlling the displacement of the compressor such that fluctuations of the pressure difference between the pressure chambers are cancelled. The first urging member urges the pressure-sensing member from one of the pressure chambers toward the other one of the pressure chambers. The second urging member urges the pressure-sensing member in the same direction as the first urging member urges the pressure-sensing member. The actuator urges the pressure-sensing member by a force, the magnitude of which corresponds to an external command.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.